Preparation of polyhalo phenols

ABSTRACT

A PROCESS IS PROVIDED FOR THE CONTROLLED HYDROLYSIS OF POLYHALOBENZENES AND, PARTICULARLY, TETRAHALOBENZENES TO POLYHALOPHENOLS IN GOOD YIELD AND PURITY. THIS IS ATTAINED BY CAUSING ALKALINE HYDROLYSIS OF A POLYHALOBENZENE CONTAINING AT LEAST THREE HALO ATOMS TO OCCUR UNDER CONTROLLED CONDITIONS WHICH INVOLVE THE PRESENCE OF AN HYDROLYSIS CONTROLLING REAGENT, A POLYHYDRIC ALCOHOL SOLVENT, HIGH CONCENTRATIONS OF RESULTANT PHENATE AT PREDETERMINED PH RANGES AND THE DIRECT RECOVERY OF SAID SOLVENT. ADVANTAGEOUSLY, THE PROCESS IS SUBSTANTIALLY FREE FROM EXPLOSION HAZARDS AND AVOIDS THE PREPARATION OF CHLORACENE-PRODUCING SUBSTANCES.

United States Patent 3,702,871 PREPARATION OF POLYHALQ PHENOLS Edwin B. Michaels, Gregory Court 06855, and John W. Lee, Glen Ave. 06850, both of Norwalk, Conn. N0 Drawing. Filed June 12, 1969, Ser. No. 832,849 Int. Cl. C07c 39/32 U.S. Cl. 26ll-623 R Claims ABSTRACT OF THE DESCLGSURE A process is provided for the controlled hydrolysis of polyhalobenzenes and, particularly, tetrahalobenzenes to polyhalophenols in good yield and purity. This is attained by causing alkaline hydrolysis of a polyhalobenzene containing at least three halo atoms to occur under controlled conditions which involve the presence of an hydrolysis controlling reagent, a polyhydric alcohol solvent, high concentrations of resultant phenate at predetermined pH ranges and the direct recovery of said solvent. Advantageously, the process is substantially free from explosion hazards and avoids the preparation of chloracneproducing substances.

The present invention relates to the manufacture of polyhalophenols from a polyhalobenzene containing at least one halogen in excess of converted product utilizing alkaline hydrolysis in the presence of an aliphatic diol and an hydrolysis controlling reagent under reflux conditions. More particularly, the invention relates to an improved alkaline hydrolysis process for converting, under reflux and in the presence of an aliphatic diol solvent, polyhalobenzenes to polyhalophenols containing at least one less halogen atom than the polyhalobenzenes being treated, while utilizing an hydrolysis controlling reagent or water entraining reagent, whereby less than 1% of the treated polyhalobenzene remains unhydrolyzed, and recovering aliphatic diol therefrom. Still more particularly, the invention is concerned with aliphatic diol recovery from a hydrolyzed reaction mixture of polyhalogenated benzenes, specifically, from the alkaline hydrolysis of l,2,4,5-tetrachlorobenzene in the presence of a solvent, such as ethylene glycol or propylene glycol, resulting in the recovery of an alkali salt of 2,4,5-trichlorophenol from a pH controlled menstruum subsequent to dis tillation of said solvent.

As is known, polyhalogenated benzenes and, particularly, 1,2,4,S-tetrachlorobenzene, can be hydrolyzed by diverse methods, each of which is not wholly satisfactory with respect to overall yield, purity and control of reaction. For instance, the alkaline hydrolysis of chlorinated benzenes utilizing caustic soda proceeds with great difiiculty except under eXteme conditions of high temperature and high pressure. To overcome such rigorous conditions, sundry alcohols as for example, methanol or glycol, have been employed in an hydrolysis mixture so as to control the rate of the polyhalobenzene hydrolysis. In this manner, only a single hydroxyl group will appear on the benzene moiety. However, the use of the monohydric alcohol, methanol, is not entirely satisfactory, since the formation of ether type derivatives, such as anisoles, readily occurs and the latter cannot be removed readily from the so-formed halophenol, thereby reducing markedly the purity of the resultant phenol. Further, the utilizaice tion of glycol as the exemplary solvent in hydrolysis environments has also been found to be unsatisfactory. This is due to the presence of large excesses of water formed from the reaction of a base, such as sodium hydroxide, with the glycol solvent to yield an ethylene glycol alkali metal derivative. In practice, moreover, the latter alkaline hydrolysis reaction is difiicult to perform due to the inhibiting action of water. Accordingly, the use of such reactions has been markedly restricted, unless adequate provisions are made for the removal of all the water prior to hydrolysis by means of an inert entraining reagent. Nonetheless, the excess entrainment of water results in the formation of large amounts of undesirable by-products. In addition, the utilization of glycol as the solvent requires that it be removed either (a) by distilling the same directly from the reaction mixture, thereby causing degradation of the hydrolyzed polyhalobenzene or (b) by effecting acidification of the reaction mixture followed by water washing so as to recover glycol solvent from the water by a series of troublesome, costly fractionations.

Notwithstanding the aforementioned difficulties, desired highly chlorinated phenols are normally quite unstable at the elevated temperatures required for obtaining quantitative yields of such phenols, namely, at temperatures above about C. In the prior practice, toxic impurities, such as diphenoxides, will form which on skin contact in amounts as little as one part per million will cause serious irritations, namely, chloracne. Further, at the elevated temperatures, side reactions occur which are all exothermic and potentially explosive. Thus, if a method could be provided to overcome all the foregoing difiiculties, it would serve to fulfill a long-felt need in the art.

It is, therefore, a principal object of the invention to provide an economical, non-hazardous hydrolysis process for converting polyhalobenzenes to alkali metal polyhalophenates and, upon sufficient acidification to the corresponding polyhalophenols, involving the utilization of a menstruum containing an alkali metal hydroxide, an aliphatic diol solvent and an hydrolyzing controlling reagent, such as an alkane of from 6 to 14 carbon atoms or mixtures thereof, whereby high yields usually ranging from 88-93% and high purity, usually not less than 99%, of polyhalophenols, are obtained. It is a further object of the invention to provide an economical method for the recovery of the aliphatic diol, such. as glycol or propylene glycol, from the hereinabove defined hydrolysis mixture containing less than 1% unreacted polyhalobenzene. It is a still further object of the invention to recover by distillation a pure halogenated phenol from a crude halogenated phenol material by admixing ammonia or ammonium hydroxide therewith. Other objects and advantages will become apparent from a reading of the ensuing description.

To this end there is provided an economical, safe and effective procedure for achieving completion of an hydrolysis reaction absent hazardous exotherms and inordinately expensive equipment by ensuring the presence of at least five mols of aliphatic diol solvent per mol of polyhalobenzene during hydrolysis. Thus, for instance, the use of a mixture comprising from 5-8 mols of glycol, 1 mol of tetrachlorobenzene and from 2.2 to 2.5 mols of sodium hydroxide results in an overall reaction mixture comprising 0.9 mol of trichlorophenol, 4 mols of glycol and 1 mol of diethylene glycol. If hydrolysis takes place in the presence of, for instance, 3 mols of glycol, there results an attack upon the glycol solvent with attendant undefined side reactions which will further result in the recovery of less than 0.9 mol of trichlorophenol, usually 0.8 mol or less, and sundry unknown compounds, while experiencing a loss of more than 2 mols of glycol solvent. Nowithstanding loss in solvent, the latter reaction mixture is an unstable one at temperatures above 150 C. and subject to dangerous toxic exotherms and hazardous explosions, particularly at temperatures of above 190 C. necessary to complete the hydrolysis reaction, namely, about 190 C. to 210 C. Surprisingly, it has been found that a stable mixture can, nonetheless, be attained prior to glycol recovery, while operating safely at temperatures of between 190 C. and 210 C. necessary to complete the reaction, thereby eliminating undesirable quantities of unreacted tetrachlorobenzene. Further, on neutralizing excess alkali metal hydroxide and on vacuum distilling glycol for the recovery of same, the hydrolysis reaction mixture has been found to be stable, even though with the removal of 4 mols of glycol the residue is concentrated to a level well above 40% concentration and a temperature above 130 C. Hitherto these conditions could not be practiced absent possible explosion and toxicity to skin.

According to the process of the invention, there is admixed in a suitable reactor equipped with agitation and condenser a polyhalobenzene, an aliphatic diol, a hydrolysis controlling reagent and an alkali metal hydroxide in amounts hereinbelow stated, at a temperature of about 160-180 C., azeotroping 2 mols of water per mol of said polyhalobenzene while maintaining the aliphatic diol in the reaction menstruum, then increasing the temperature to from about 190 C. to about 210 C. so as to complete the hydrolysis reaction and removing substantially all of the hydrolysis controlling reagent. Less than 1% of the polyhalobenzene remains in the hydrolyzed medium. The latter medium is neutralized to remove excess alkali metal hydroxide by acid addition to a pH between 11 and 13, vacuum distilling resultant neutralized medium to remove aliphatic diol therefrom and, thereafter, recovering 2,4,5-trichlorophenol in good yield and purity.

It has been found unexpectedly that, where the afore mentioned critical steps are not observed, the recovery of both polyhalophenol and aliphatic diol solvent cannot be readily realized. Expensive techniques for solvent recovery, together with imminent explosion hazards and side reactions resulting in impurities which are responsible for chloracne, are noted. Thus, for instance, heating a reaction mixture as defined above to reflux at temperatures between 160 C. and 180 C. at a rate such that 2 mols of water are removed, results in a reaction menstruum which is not spontaneously explosive, but is controllable when the reaction vessel is heated to from 190 C. to about 210 C. At the latter temperature range, the reaction is completed.

The aforementioned temperature range is critical to obtain less than 1% of unhydrolyzed polyhalobenzene. This is highly desirable to prevent clogging of the condenser when an attempt to recover the aliphatic diol solvent is made. Moreover, if a reaction mixture containing more than 1% of unhydrolyzed polyhalobenzene and the desired hydrolyzed product were acidified, the unhydrolyzed polyhalobenzene would be present as a diflicult-to-remove impurity.

Illustrative of the polyhalobenzenes containing three to six halogen atoms which can be hydrolyzed by the process of the invention are: 1,2,4,S-tetrachlorobenzene, 1,2,3,5- tetrachlorobenzene, 1,2,4-trichlorobenzene, 1,2,4-tribromobenzene, or 1,2,3,4,5,6-hexachlorobenzene.

Although the process of the invention has been exemplified hereinbelow utilizing l,2,4,5-tetrachlorobenzene, any of the recited polyhalobenzenes may similarly be so employed.

Exemplary of the aliphatic diols contemplated herein are: glycol or propylene glycol, in amounts ranging from not less than 5 to about 8 or more mols and, preferably 6 mols, per mol of polyhalobenzene.

As the base or alkali metal hydroxide reactant contemplated, there is employed sodium hydroxide, potassium hydroxide or lithium hydroxide. Usually, an amount ranging from 2.2 to 3 mols, and, preferably, 2.5 mols per mol of polyhalobenzene is a good practice.

Illustrative hydrolysis controlling reagents which can be mentioned are: (a) an alkane containing from 6 to 12 carbon atoms, or mixture thereof, namely, hexane, heptane, octane, nonane, decane, undecane, dodecane, deordorized kerosene or mineral spirits having a boiling point range between 160 C. and 180 C. or (b) a monoor dialkyl benzene containing from 2 to 4 carbon atoms in the alkyl substituent, such as xylene o-ethyl benzene, n-propyl benzene, o-isobutyl benzene, 1,4 diethylbenzene, 1-ethyI-4-n-propyl benzene, n-butylbenzene, or halogenated benzenes, such as o-dichlorobenzene and isomers thereof, in amounts ranging from 0.01 mol to 0.5 mol, and, preferably, 0.07 mol per mol of polyhalobenzene to be treated.

The aforementioned four components of the mixture are all admixed in a suitable reactor containing condenser under agitation at a temperature below reflux, usually between C. and C. Hydrolysis then proceeds in two heating stages, namely, under reflux at temperatures ranging from about C. to about C. for a time sufiicient to collect as a distillate 2 mols of water and then completing the hydrolysis at a temperature between about C. and about 210 C., usually between 0.3 and 3 hours.

Hydrolyzed mixture substantially free from unhydrolyzed polyhalobenzene is next acidified with any mineral acid, such as hydrochloric acid or sulfuric acid, so as to reduce the pH of the hydrolysis mixture from about 14 to from 11 to 13, and preferably to a pH from 12 to 12.5. Thereafter, the so-pH adjusted hydrolyzed mixture is subjected to vacuum distillation, preferably at from about 5 mm. Hg to about 30 mm. Hg, at a base temperature of from 100 C. to 170 C. to recover the aliphatic diol of adequate grade and purity for reuse.

Resultant residue remaining in the distillation flask is admixed with suflicient water to dissolve the alkali metal phenate formed during hydrolysis. To the water layer is added suflicient mineral acid, such as sulfuric acid, to further reduce the pH of the mixture to from 4 to 4.5, whereby the recovered alkali metal phenate is converted to the corresponding halogenated phenol. Two layers form. The upper water layer is discarded, but the lower layer containing the phenol is washed several times with water at temperatures ranging from about 65 C. to about 100 C. to recover desired halogenated phenol.

To ensure purity of latter product, there is admixed miniscule amounts of from 0.05 mol to 0.5 mol of ammonia or ammonium hydroxide to the recovered phenol mixture, so as to neutralize any residual mineral acid therein. The latter mixture is dehydrated and distilled at from 10 mm. Hg to 20 mm. Hg pressure to recover at least 99% pure halogenated phenol in yields ranging from above about 88% to about 93% of theory. Advantageously, the utilization of ammonia or ammonium hydroxide is applicable to the purification and recovery of any halogenated phenol prior to vacuum distilling the latter relatively crude halogenated phenol.

The following examples are presented as merely illustrative and are not to be taken as being limitative of the invention. Unless otherwise stated, any parts given are by weight.

EXAMPLE 1 To a stainless steel reaction vessel equipped with condenser and stirrer, are admixed with agitation 0.07 mol of mineral spirits boiling between 160 C. and 180 C., 6 mols of glycol, 1 mol of tetrachlorobenzene and 2.5 mols of sodium hydroxide, While heating to a temperature of about 140 C. The mixture is next heated to reflux temperatures ranging from between 160 C. and 180 C. for about 0.75 hour to 3 hours to distill a binary azeotropic mixture of Water and mineral spirits of 4/6 volume ratio and collecting 2 mols of water, While returning the mineral spirits to the reaction. The heating rate is so regulated as to maintain within the condenser a vapor temperature of from 95 C.97 C. At higher temperatures, say at 100 C., glycol is found to be entrained in the binary azeotrope in amounts usually in excess of 5%. If, as a result of such glycol removal, the hydrolysis mixture falls below the critical 5 mols, there is created a potentially explosive environment.

With the removal of 2 mols of water, the hydrolysis reaction is not spontaneous. However, the hydrolysis of the tetrachlorobenzene is about 90% complete. To complete the hydrolysis, such that less than 1% of the treated tetrachlorobenzene remains unreacted, the temperature is next increased to between 190 C. and 195 C. for from 0.3 to 3 hours. All the mineral spirits as Well as any residual free Water are thereby distilled. Where amounts of tetrachlorobenzene in excess of 1% remain in the hydrolyzed mixture, the direct recovery of glycol by distillation therefrom cannot be readily achieved because the tetrachlorobenzene clogs or blocks the condenser thereby prohibiting egress and recovery of the glycol solvent.

Upon completion of the hydrolysis reaction in the substantial absence of tetrachlorobenzene, there is next added about 0.4 mol equivalents of sulfuric acid to neutralize the mixture containing excess base to a pH of from 12 to 12.5. The critically pH adjusted mixture is next subjected to vacuum distillation at from about 8 mm. to 10 mm. Hg pressure at a kettle temperature between 100 C. and 170 C., whereby the glycol present in the mixture is recovered for reuse.

Residual sodium salt of 2,4,5-trichlorophenol, free of glycol, is next acidified with sulfuric acid to a pH of 4.5

and twice washed with hot water to recover 200 parts of crude 2,4,5-trichlorophenol. To the latter is next added 4 parts of ammonium hydroxide. The latter neutralizes any entrained acid and forms miniscule amounts of the corresponding ammonium phenate.

Resultant mixture is next dehydrated and distilled under vacuum and there is collected 181 parts of 2,4,5-tri chlorophenol, equivalent to a yield of 93% and having a crystallizing point of 64.5 C.

Similar results are obtained when substituting potassium hydroxide for sodium hydroxide, propylene glycol for glycol, and xylene or dichlorobenzene for mineral spirits in the procedure of Example 1, above.

EXAMPLE 2 The hydrolysis procedure of Example 1 is followed in every material aspect except there are admixed 4 mols of glycol, 3.5 mols of sodium hydroxide, 1 mol of tetrachlorobenzene and 0.25 mol of xylene as the hydrolysis mixture. After initial water and xylene removal at a temperature of 155 C. instead of 160 C., the reaction medium became exothermic and the temperature rose to 250 C. within five seconds. The resultant hydrolysis reaction which was uncontrollable was terminated at this point while noting a tarry mass as a residue.

In the process of the present invention the aforementioned conditions for effecting hydrolysis involving a two-step heating range, namely one from (a) 160 C. to 180 C. and (b) 190 C. to 210 C. with the subsequent recovery of the aliphatic diol solvent, are all critically interrelated. Thus, whereas other analogous systems exhibit hazardous exothermic conditions at temperatures within the latter reaction range, the present reaction system maintains thermal stability at temperature even as high as 240 C. However, at the latter temperatures glycol solvent is lost and degradation reactions and formation of toxic compounds as well are all possible. Therefore, the times and temperatures herein recited are critical and must be maintained. Further, in the absence of glycol or propylene glycol hydrolysis, say hydrolysis in methanol solvent, temperatures in excess of C. so as to effect methanol solvent recovery will cause exotherms with attendant formation of toxic diphenoxides which appear to cause chloracne. To avoid such exotherms in hydrolysis reactions employing methanol, the concentration of the resultant phenate must be carefully and critically controlled to levels below 40% usually accomplished by the addition of large volumes of water prior to recovery of methanol by steam distillation. Advantageously, the difficulties of the prior procedures are overcome with resultant safety and effectiveness to obtain high purity and yield of a desired polyhalophenol.

We claim:

1. A process for the preparation of a polychlorophenol or polybromophenol containing one less halogen atom than the corresponding polychlorobenzene or polybromobenzene from which it is prepared by alkaline hydrolysis which comprises the steps of:

(a) admixing 1 mol of polychlorobenzene or polybromobenzene containing from 3 to 6 halogen atoms, from 2.2 to 3 mols of an alkali metal hydroxide, from 5 to 8 mols of an aliphatic diol containing from 2 to 3 carbon atoms and from 0.01 to 0.5 mol of an hydrolysis controlling reagent selected from the group consisting of alkanes of from 6 to 12 carbon atoms, monoalkyl benzene and dialkyl benzene, said alkyl having from 2 to 4 carbon atoms,

(b) agitating the reaction mixture of (a) under reflux at a temperature between C. and C.,

(c) maintaining said reflux until 2 mols of Water are withdrawn from the reaction mixture while retaining substantially all the hydrolysis controlling reagent and the aliphatic diol therein,

(d) increasing the temperature of reaction mixture to a temperature of from about C. to about 210 C. to remove said hydrolysis controlling reagent and effect completion of the hydrolysis of polyhalobenzene whereby less than 1% of unhydrolyzed polychlorobenzene or polybromobenzene remains in the reaction mixture,

(e) adjusting the pH of the latter mixture to a pH from (f) vacuum distilling resultant pH-adjusted reaction medium to remove all the aliphatic diol therefrom, and

(g) recovering a polychlorophenol or polybromophenol having one less halogen atom than is present in the polychlorobenzene or polybromobenzene treated.

2. A process according to claim. 1 in which the polychlorobenzene is 1,2,4,5-tetrachlorobenzene.

3. A process according to claim 1 in which the hydrolysis controlling reagent is mineral spirits.

4. A process according to claim 1 in which the hydrolysis controlling reagent is xylene.

5. A process according to claim 1 wherein the alkali metal hydroxide is sodium hydroxide.

6. A process according to claim 1 wherein the alkali metal hydroxide is potassium hydroxide.

7. In a process according to claim 1 for the preparation of a polychlorophenyl or polybromophenol containing one less halogen atom than the polychlorobenzene or polybromobenzene from which it is prepared utilizing alkaline hydrolysis in the presence of an aliphatic diol solvent, the improvement for the recovery of the aliphatic diol solvent which comprises the steps of: adjusting the pH of the hydrolyzed reaction medium to a pH between about 1 1 and 13 and thereafter vacuum distilling the mixture to recover as a distillate aliphatic diol solvent.

8. A process according to claim 7 wherein the pH of the mixture is 12.5.

8 9. A process according to claim 7 wherein the aliphatic mixture under vacuum to recover substantially pure polydiol solvent is glycol. chlorophenol or polybromophenol in good yield.

10. In a process according to claim 1 for the preparation of polychlorophenol or polybromophenol containing one less halogen atom than the polychlorobenzene or References Cited UNITED STATES PATENTS polybromobenzene from which it is prepared utilizing 2,803,670 8/1957 Galat 260-623 R alkaline hydrolysis in the presence of an aliphatic solvent, 2,872,461 2/ 1959 *Mattner 260-623 R the improvement for the recovery of said polychloro- 2,509,245 5/ 1950 NikaWitZ et a1 260-623 R phenol or polybromophenol which comprises the steps 10 3,417,150 12/1968 Bondy et a1 R of; sub ecting the g lycol free reactionmixture to mineral BERNARD HELEN, Primary Examiner acid acidification, incorporating therein a small amount of ammonia or ammonium hydroxide, and distilling the LONE Asslstant Exammer 

